In present-day internal combustion engines with direct gasoline injection, the fuel supply takes place in an inherently known manner with fuel pressures up to 200 bar. In individual regions of the direct gasoline injection, as, for example, during spray-form combustion processes or in highly supercharged internal combustion engines, still higher pressures even occur. In order to transmit the forces required for producing these pressures from a camshaft or a crankshaft of the internal combustion engine to a high pressure pump, the pump tappets generally known to be used in these pumps have to be supplied with lubricating oil from the oil circuit of the internal combustion engine.
If an increased leakage now occurs between the gaskets disposed in the oil circuit and those disposed in the fuel circuit, fuel with the prefeed pressure of a low pressure circuit disposed in the internal combustion engine can thus enter into said oil circuit. The consequent dilution of the lubricating oil (engine oil) of the internal combustion engine is predetermined in the pre-published German patent applications DE 10 2004 033 413 A1 and DE 10 2004 033 414 A1.
In the aforementioned German patent DE 10 2004 033 413 A1, an oil dilution signal is notably ascertained, which is a measurement for the volume of the oil dilution, which has ingressed into the engine oil of the internal combustion engine as a result of at least one fuel afterinjection. The stated afterinjection serves the purpose of introducing uncombusted fuel as the combustible into the exhaust gas zone of the internal combustion engine. Said uncombusted fuel reacts exothermally to heat an exhaust gas treatment apparatus. It is thereby possible to ascertain the oil dilution solely from existing operating parameters of the internal combustion engine.
In the aforementioned German patent DE 10 2004 033 414 A1, it is additionally proposed to take said oil dilution signal into account when the oil level of the engine oil of the internal combustion engine is ascertained. It is thereby possible to be able to ascertain the measurement for the oil level solely from existing operating parameters of the internal combustion engine.
Said oil dilution leads to a shortened service life of the internal combustion engine on account of the degraded lubrication.
Oil quality sensors are already used for monitoring the quality of the oil. An increased fuel ingress, which was previously described, leads by means of these sensors to drastically shortened oil change intervals, which, of course, prevent damage to the internal combustion engine. However, on account of the shortened service intervals and the increased expenses, which go along with them, acceptance of the stated internal combustion engines with direct fuel injection by the driving public is rather impeded.
Moreover, due to the additional installation costs for these oil quality sensors, said sensors are only used in internal combustion engines of the upscale vehicle class and are for this reason not yet widely used.
Furthermore, the detection of a leaky high pressure pump is also not unambiguously possible on the basis of said oil quality sensors.